1. Field of the Invention
The present invention relates to a plasma CVD apparatus for processing a semiconductor substrate, and particularly it relates to a semiconductor substrate-supporting mechanism for supporting a semiconductor substrate which is loaded on a susceptor in mid-air when the substrate is conveyed.
2. Description of the Related Art
Conventional substrate processing apparatuses comprise a plasma reaction chamber, a load lock chamber where multiple wafer substrates are loaded on a cassette board and held, and a substrate transfer chamber with a substrate-conveying mechanism to link both the plasma chamber and the load lock chamber.
Semiconductor substrates are carried into and carried out of the reaction chamber by a reciprocating blade which is mounted at the tip of the arm of said substrate-conveying mechanism between the load lock chamber and the reaction chamber. To prevent moisture in the atmosphere and particle contamination, each chamber is separated by a gate valve and continuously vacuum-exhausted, and each gate valve of each of the chambers is set to open only when a semiconductor substrate is conveyed.
To lift a semiconductor substrate loaded on a susceptor within the reaction chamber by a blade, a space for inserting the blade between the semiconductor wafer and the susceptor is necessary. In the case of the conventional apparatus, multiple through-holes are provided for the susceptor and the apparatus has a structure in which a pin is inserted into this through-hole, the tip of the pin moves out and in from the susceptor surface with an up-and-down (vertical) movement of the susceptor. This pin protrudes from the susceptor at the time of transfer to suspend a semiconductor wafer in mid-air, and it is completely seated within the susceptor at the time of processing.
There are two types of this conventional method of supporting a semiconductor substrate with a pin.
One method is a type to fix one end of the pin to the base of a reaction chamber. Another is a method in which the pin is supported and suspended within the through-hole of the susceptor. The latter type is mainly used with a rotatable type of susceptor apparatus. As the susceptor descends and moves, one end of the pin contacts a pad provided at the reaction chamber base, and the pin stands upright on the pad and supports a semiconductor substrate through the through-hole.
The above-mentioned two conventional methods of supporting a semiconductor substrate with a pin are faulty in the following points: First, in the case of a lower-end fixed type in which one end of the pin is fixed at the reaction chamber base, a position of height direction of the tip of the pin has to be determined exactly for the following reasons: the height of the pin from the susceptor surface at the time of transfer must be sufficient to receive the blade. If the tip of the pin is not completely seated within the through-hole at reaction processing, the semiconductor substrate does not fully contact the susceptor and is partly suspended in mid-air. If the pin protrudes from the susceptor surface when plasma cleaning of the reaction chamber is performed, there is the further possibility of generating an arc due to the concentration of discharged energy on the pin. This arc causes serious damage not only to the pin but also to the showerhead surface. If the pin is retracted considerably, plasma discharge concentrates on the lip portion of the through-hole as well and damages a protective coat or coating film of a showerhead surface that faces the portion. This creates a risk that these films that thus come off and scatter inside the reaction chamber and cause impurity contamination. Similarly in the state where the pin is retracted considerably from the susceptor surface within the through-hole, active species caused by plasma discharge furthermore forces its way into the inner part of the susceptor device and damages the susceptor, a heater set up below it, the pin, and its fixing structure.
In this way, in the case of the conventional lower-end fixed type devices, the position of a height direction of the pin tip has to be exactly determined, and work time, therefore, becomes longer.
Additionally, because the pin has as conventionally been manufactured of aluminum alloy, its length changes with thermal expansion. Height adjustment at actual temperature used (200xcx9c300xc2x0 C. (392xcx9c572xc2x0 F.)) is very risky and difficult. Furthermore, at a temperature of 300xcx9c400xc2x0 C. (572xcx9c752xc2x0 F.), the mechanical strength of the pin deteriorates and it is also insufficient to support a wafer with a large diameter (300 mm). For this reason, the pin deforms in the consecutive processes of supporting the wafer. As this happens, device down time required for replacement of expendables becomes longer. As a result, yield and productivity drop.
In the case of a suspension type wherein a pin is accommodated within a through-hole of a susceptor, to receive a thick blade when supporting a 300 mm wafer with high weight, a distance that the pin protrudes from the susceptor surface becomes longer and support becomes unstable.
Further, this pin is electrostatically attracted to the backside of a semiconductor wafer which has been plasma processed and electrically charged, and there is a risk that the pin is supported with the wafer when the wafer is conveyed. In this case, the pin will drop during transfer of the wafer due to impact from a transfer robot. As a result, it is damaged and this causes particle contamination.
Consequently, an object of the present invention is to provide a substrate-supporting mechanism for which pin height can be adjusted easily.
Another object of the present invention is to provide a substrate-supporting mechanism for which replacement of expendables such as pins is easy.
A further object of the present invention is to provide a substrate-supporting mechanism that can stably support a semiconductor substrate with a large diameter.
An additional object of the present invention is to provide a substrate-supporting mechanism for which the tip portion of the pin is not electrostatically attracted to the backside of a semiconductor wafer.
To achieve one or more of the above-mentioned objects, the present invention provides an apparatus for processing a semiconductor substrate, comprising: (a) a reaction chamber; (b) a susceptor within the chamber for supporting a substrate thereon when processed, said susceptor having at least three vertical through-holes at designated positions; (c) substrate-supporting members slidably fitted in the respective through-holes, each substrate-supporting member having an upper end and a lower end, each substrate-supporting member being reciprocally slidable along the through-hole between an upper position where the upper end protrudes from the susceptor and a lower position where the upper end does not protrude from the susceptor, wherein when the substrate-supporting members are at the upper position, the substrate is supported apart from the susceptor by the upper ends of the substrate-supporting members; and (d) pins corresponding to the respective substrate-supporting member, each pin having an upper end pushing upward the substrate-supporting member to move the substrate-supporting member to the upper position, where the upper end of the pin and the lower end of the substrate-supporting member are detachably fitted to restrict further upward movement of the substrate-supporting member, each pin being retracted downward to detach the upper end of the pin from the substrate-supporting member positioned at the lower position.
In an embodiment, the pins are fixed in the chamber, and the susceptor is vertically movable to move the substrate-supporting members between the upper position and the lower position. In the above, a moving device for mechanically moving the susceptor vertically may be provided. In another embodiment, a pin-fixing structure is provided at a base of the chamber, wherein each pin has a lower end fixed to the pin-fixing structure.
The present invention can equally be adapted to a method for processing a substrate using the above-mentioned apparatus. The method may comprise: (i) loading a substrate in the reaction chamber, wherein the substrate is supported apart from the susceptor by the substrate-supporting members at the upper position; (ii) moving downward the substrate-supporting members to the lower position by movement of the pins relative to the susceptor, wherein the substrate is placed on the susceptor; (iii) processing the substrate; (iv) moving upward the substrate-supporting members to the upper position by movement of the pins relative to the susceptor, wherein the substrate is supported apart from the susceptor by the substrate-supporting members at the upper position; and (v) unloading the processed substrate from the chamber.
In the above, in an embodiment, the method further comprises cleaning the chamber when the substrate-supporting members are at the lower position. In another embodiment, the vertical movement of the substrate-supporting members relative to the susceptor is conducted by vertically moving the susceptor whereas the pins are held still.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.